title: Persistent petrosquamosal sinus: high incidence in cases of complete aplasia of the semicircular canals.
abstract: OBJECTIVE
  To determine the frequency and to describe the morphologic characteristics and associated skull base anomalies of the petrosquamosal sinus (PSS) in cochlear implant candidates with complete aplasia of the semicircular canals (SCCs).
  
  
  METHODS
  Ethics committee approval was obtained. Index cases were retrospectively selected from an electronic database in which all inner ear malformations observed in patients presenting to a tertiary referral center between 1995 and 2010 were collected. Computed tomography (CT) data were reviewed by neuroradiologists. Clinical consequences of the neuroradiologic findings were analyzed. The Pearson χ(2) test and the Mann-Whitney U test were used to determine significant differences between the number of PSSs observed in cases of complete aplasia of the SCCs and the number observed in cases of other types of inner ear malformations.
  
  
  RESULTS
  Inner ear malformations were analyzed in 241 patients. Thirty-one patients (13%) with bilateral SCC aplasia were identified. Among 31 patients, a uni- or bilateral PSS was observed in 25 (81%). In the ears with SCC aplasia, a PSS was observed in 40 (65%) of 62. The three cases in which these PSS occupy the largest area correlate with bilateral absence of the jugular foramen. In seven of eight ears with a PSS, the PSS inhibited surgical exposure or resulted in accidental opening of the PSS during surgery. In all other patients with inner ear malformations, a PSS was observed in 39 (9%) of 412 ears only.
  
  
  CONCLUSIONS
  The PSS presents a risk for cochlear implant surgery that can be detected by the neuroradiologist in advance. Venous CT angiography is advisable in certain cases. The previous assumption that a persistent PSS is encountered more frequently in cases of skull base deformity can be affirmed in the special situation of complete aplasia of the SCCs.
authors.affiliation: Department of Diagnostic and Interventional Neuroradiology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany. Giesemann.Anja@mh-hannover.de
authors.forename: Anja M
authors.initials: AM
authors.lastname: Giesemann
authors.forename: G Friedrich
authors.initials: GF
authors.lastname: Goetz
authors.forename: Jürgen
authors.initials: J
authors.lastname: Neuburger
authors.forename: Thomas
authors.initials: T
authors.lastname: Lenarz
authors.forename: Heinrich
authors.initials: H
authors.lastname: Lanfermann
mesh_terms: D000293:Adolescent; D002550:Cerebral Veins / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D016009:Chi-Square Distribution; D002648:Child; D002675:Child, Preschool; D019929:Cochlear Implantation; D003392:Cranial Sinuses / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D005260:Female; D006319:Hearing Loss, Sensorineural / Q000209:etiology* / Q000601:surgery; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D012189:Retrospective Studies; D012665:Semicircular Canals / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed / Q000379:methods*